As described in copending patent application No. 299,306 filed April 10, 1981, now abandoned, one method of leaching out the bitumen oil content of raw oil sands is to agitate the oil sands gently with relatively large quantities of hot water, the lumps of oil sands being broken up by thermal action and the bitumen oils released. It is further explained in that application that the recovery of the bitumen oils is facilitated if, firstly, the liquid and solids are discharged separately from the leaching process, and, secondly, clay and other dross included in the oil sands are not disintegrated during that process.